The big broadcast TV networks are moving to get paid for commercials that viewers see even if it is a week after they originally air, a development with major implications for the roughly $70 billion TV advertising marketplace.

In a major shift, all the major networks—NBC, ABC, Fox and CBS—have reached agreements with a major media-buyer, GroupM, to change how audiences are counted for the purposes of advertising deals, people familiar with the matter say. Under the pacts, deals for prime-time TV shows will be based on...

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The big broadcast TV networks are moving to get paid for commercials that viewers see even if it is a week after they originally air, a development with major implications for the roughly $70 billion TV advertising marketplace. Steven Perlberg joins MoneyBeat. Photo: "Modern Family"/ABC.